dir.c (join_path_from_pattern): check NULL from malloc

Coverity Scan points out that all the return values of GLOB_ALLOC_N are
NULL-checked except this call.

dir.c

@@ -2072,9 +2072,11 @@ join_path_from_pattern(struct glob_pattern **beg)
 	if (!path) {
 	    path_len = strlen(str);
 	    path = GLOB_ALLOC_N(char, path_len + 1);
+            if (path) {
                 memcpy(path, str, path_len);
                 path[path_len] = '\0';
             }
+        }
         else {
 	    size_t len = strlen(str);
 	    char *tmp;